There is a growing awareness among wildlife biologists and
conservationists that relatively benign human activities or even our mere
presence adversely affects many wildlife species. Those activities need not
be hunting, chasing, shooting, destroying habitat, or in any way overtly
harassing the wildlife, but simply being present.
Human Disturbance of Wildlife
Chapter III of the handbook Managing Development for People and
Wildlife, prepared by Clarion Associates and the Colorado Division of
Wildlife, states: "Human activities in or near wildlife habitat may cause
some animals to alter their activity and feeding patterns. Although such
alterations may seem relatively harmless at the time to the casual observer,
they may have non-trivial consequences for the animal. For example, stress
that results from human disturbance may lead to increased susceptibility to
disease, reduced reproductive output in some species, or abandonment of the
area temporarily or permanently."
The handbook continues: "When surprised or threatened, wildlife react
in a number of ways, occasionally "playing possum" or assuming a defensive
posture, but more often fleeing. Active responses to human disturbance are
typified by the animal's running or taking flight in order to escape. This
sort of response is associated with a number of profound physiological
adjustments, such as increased heart and respiration rates, elevated blood
sugar, increased blood flow, and increased body temperature -- in other
words, stress. Energetic costs associated with an active response to human
disturbance may have serious consequences for animals. This is especially
true during critical times of the year, such as the postnatal period for
mammals or the breeding period for birds, when an animal's energy reserves
are already depleted and further stress may result in diminished
reproductive output. For birds, disturbance may result in slower growth or
premature fledgling for nestlings, and in nest evacuation or abandonment by
the parents. Even if the parents eventually return to the nest, the eggs or
young may be lost to predators in their absence."
Last year, the Ecological Society of America reported on research
conducted by wildlife biologists Robert Steidl of the University of Arizona
and Robert Anthony of Oregon State University about the effects of human
visits to the Gulkana National Wild River in Alaska upon resident bald
eagles. The article reported: "Adult eagles decreased some activities by as
much as 59% per day when humans were nearby. In addition, the percentage of
time that they left their nesting area unattended increased by 24%. ...
[W]hen humans were near the nests, the number of feeding bouts at the nest
decreased by 20% per day. Further, the amount of prey consumed by the eagles
decreased by an average of 29% per day."
Habituation and Attraction
Some wild animals become accustomed (habituated) to human presence and
activities, and a few may even approach people to seek food. Although such
animals may appear to adapt well or to even prosper in the presence of
people, they usually alter their normal foraging patterns and other
behaviors. They may abnormally concentrate into a small area, scatter other
animals, spread diseases, or directly imperil other species. For example,
corvids (Steller jays and ravens) have learned to scavenge food that
visitors bring into old-growth redwood forests along the California coast.
While in the dense forests they would normally avoid, the corvids will prey
on any marbled murrelets (endangered under the California ESA) they may
Wild animals that eat food from humans, whether supplied intentionally
or unintentionally, frequently suffer nutritional deficiencies, become
abnormally fat, or refrain (as with some birds) from normal migration.
Animals that approach people bring risks to both themselves and the people,
as is the case with black bears in Yosemite National Park. Although the
effects might not be immediately evident, the response of wildlife to human
presence disturbs the dynamics of biological communities.
Evolution of North American Wildlife
One of the reasons for the stress reactions of the native wildlife of
North America to human presence and activities may be that we are a recent
phenomenon in their evolutionary history. They simply have not had enough
time to evolve effective strategies to cope with us.
Effects of Human Activities on Habitat
Beyond the direct effects upon wildlife, human activities affect the
ecosystems where animals live. As a recent publication by the Montana
Chapter of the Wildlife Society states: "The most obvious impact of human
activity on the land is to the soil surface itself. Effects on soils, in
turn, determine the presence (or absence) and the characteristics of [the]
vegetation supported (species composition, vigor, productivity, and
structure). Composition and structure of vegetation, in turn, determine the
suitability of the site to serve as habitat for wildlife species closely
tied to vegetative composition and/or structure. Habitat suitability for
small mammal or amphibian species, for example, determines whether the
habitat or landscape unit can support larger, more visible species,
People may unintentionally carry seeds, spores, or other material on
their person, equipment, or vehicles that may spread exotic weeds or other
invasive plant species. Conservation biologists warn that exotics may some
day overtake habitat destruction as the leading cause of species
endangerment and extinction.
From all the proceeding, it becomes obvious that current reserves --
such as wildlife refuges, wilderness areas, open space preserves, and
parks -- do not provide sufficient sanctuary for native wildlife. Thus, we
need a new and creative approach to help ensure their welfare.
The Wildlands Design
One good approach to minimize human disturbance of wildlife is the
design championed by the Wildlands Project, whereby wildlife managers
designate a core habitat area where human visitation and activities are
severely restricted. A buffer area, where people may engage in customary
wilderness recreation, surrounds the core. Some managers even designate a
layer of concentric buffers, with progressively greater human presence and
activity in the outer layers. Where feasible, wildlife corridors may link
otherwise isolated habitat areas.
The Human-Free Habitat Resolution
The Human-Free Habitat Resolution carries the Wildlands Design one
step further by proposing that the Sierra Club advance the idea that some
habitat areas be reserved exclusively for wildlife.
Nothing in the resolution states or implies that people be denied any
space that is essential to meet their needs. Good candidate areas must be
relatively remote and as near to wilderness conditions as possible. They
must have high-quality habitat that is capable of supporting self-sufficient
populations of native wildlife. Areas where, for example, ungulates could
populate beyond what the range could support would be unsuitable. In
addition, we would not propose areas with significant development, nor would
we advocate depriving people of important recreational opportunities.
Summary Requirements of Good Candidate Areas
Ø Good candidate areas would likely be relatively remote or exist where
human activities have been light or highly restricted. They might include
uninhabited islands, protected watersheds, and abandoned military bases.
Ø Good candidate areas would support a rich diversity of native wildlife
species or would provide critical habitat for rare or endangered species.
Ø Good candidate areas would carry high-quality habitat for the resident
wildlife species. Such habitat would be capable of supporting
self-sustaining wildlife populations that will not degrade the ecosystem.
Ø Good candidate areas would have suitable contiguous habitat,
preferably with corridors, that allow animals to migrate.
Ø Good candidate areas would be free of any paved or well-traveled
Ø Good candidate areas would be relatively free of human artifacts.
Ø Good candidate areas would be relatively free of exotic plants,
animals, and fungi.
Some Candidate Areas May Lie in Existing Preserves
Some candidate areas may exist within frequently visited wilderness or
open space preserves. Although there may be hiking trails throughout them,
people do not traverse all existing acres. Indeed, signs often tell people
to stay on the trails, and some areas are specifically designated as "no
entry" because of restoration work, the need to protect sensitive species,
or other reasons.
For example, "full cave closure" to all visitor access is one of the
management options that the National Park Service is considering in order to
protect the colony of the endangered Townsend's big-eared bats in the Bear
Gulch Caves at Pinnacles National Monument in California.
An Example of a Good Candidate Area
My favorite candidate for human-free habitat is Red Rock, which stands
in San Francisco Bay near the Richmond-San Rafael Bridge. The rock supports
a rich diversity of sea birds, such as gulls, herons, egrets, and endangered
brown pelicans. According to the San Francisco Chronicle (06/07/2001),
the rock carries a price tag of $10 million and, for various, reasons, would
be difficult to develop. Clearly, Red Rock would be of extremely limited
value to humans, probably used only as an infrequently visited vacation stop
for a few people wealthy enough to buy the rock and build something on it.
Perhaps some conservation organization or consortium will raise the funds,
buy it, then leave it alone. The wildlife will manage just fine.
Implementation would be on a site-specific basis, likely following
appropriate public hearings, reviews, and environmental impact reports.
Those processes would address potential problems and issues -- such as
enforcement, restoration needs, or the presence of invasive species or human
artifacts -- applying to the site in question.
Concerns about Political Opposition
Some Sierra Club members have expressed the concern that the provision
to bar all people from some habitat areas would elicit widespread political
opposition to the resolution. Yet, geographical prohibitions on human
activities are common, and our society widely accepts the concept of "no
trespassing." Would the average person care if no people may enter a
habitat area or if only a few or even one person (a wildlife manager, for
example) may enter it? The important issue to the individual is that she or
he may not enter. Because that issue is already common in our society, the
Human-Free Habitat Resolution should raise no new objections.
The Human-Free Habitat Resolution is compatible with the Sierra Club's
mission, guidelines, and policies. For example, section 3(a) of the Club's
Wildlife and Native Plants Policy states:
"Within natural ecosystems, the Sierra Club believes natural diversity and
abundance of wildlife and native plants should be ensured by means that
involve a minimum of overt human interference."
It follows, therefore, that the "minimum of overt human interference"
can be zero if the ecosystem and biological community do not require it.
The resolution does not discourage appropriate restoration or rehabilitation
work in those ecosystems that need it.
Raise Public Awareness
Once before the public, the Human-Free Habitat proposal may spark a
serious discussion within society and among wildlife professionals. Such
discussion may raise awareness in people about the particular needs of
wildlife and may lead people to understand the perspective of other species,
as those beings struggle to live in an increasingly human-dominated world.
Edward M. Smith
San Jose, California
 Duerksen, Hobbs, Elliot, et al, Managing Development for People and
Wildlife: A Handbook for Habitat Protection by Local Governments;
 The Ecological Society of America, No Picnic for the Birds: Examining
the Effects of Human Activity on Bald Eagles; March 2, 2000,
 Caryla J. Larsen, Report to the Fish and Game Commission: A Status
Review of the Marbled Murrelet in California, June 1994, page 2.
 Montana Chapter of the Wildlife Society, Effects of Recreation on Rocky
Mountain Wildlife: A Review for Montana, September 1999, page 1.11
 Soulé, Michael E. and Orians, Gordon H., eds., Conservation Biology
Research Priorities for the Next Decade, Island Press, Washington DC, 2001.
 San Francisco Chronicle, Island Full of Headaches for $10 Million: Red
Rock, Bay's Last Private Isle, Would not be Easy to Develop, June 7, 2001,